METAL RECOVERY PROCESS FROM OXIDE MINERALS.

Abstract

A process for the recovery of valuable metals from oxide minerals, particularly polymetallic nodules, is disclosed. The process is suitable for the recovery of Cu, Co, Ni, Fe, and Mn, which are the main metals of interest in these polymetallic nodules. Among other features, the present process is characterized by the handling of Fe, which is dissolved and retained in solution until the crystallization stage instead of being removed in an earlier stage. A mixed Mn-Fe residue is obtained, which, after heat treatment, yields a Mn-Fe oxide suitable for the steel or manganese industries. Excellent yields of Cu, Co, and Ni are obtained, while the Fe is leached and recovered along with the Mn.

Description

METAL RECOVERY PROCESS FROM OXIDE MINERALS This disclosure relates to a process for recovering valuable metals from oxide minerals, specifically from polymetallic nodules. Polymetallic nodules, also called deep-sea nodules or deep-sea manganese nodules, are rock concretions formed by concentric layers of iron and manganese oxides on the ocean floor. The disclosed process is suitable for the recovery of Cu, Co, Ni, Fe and Mn, which are the main metals of interest in such polymetallic nodules. To date, the most economically significant nodules have been found in the Clarion Clipperton Fracture Zone (CCFZ). Nodules in this area typically contain 27% Mn, 1.3% Ni, 1.1% Cu, 0.2% Co, 6% Fe, 6.5% Si, and 3% Al. Other elements of economic interest include Zn, Mo, and rare earth elements. Additional important deposits have been found in the Penrhyn Basin near the Cook Islands, the Peru Basin in the southeastern Pacific, and in a region known as the Indian Ocean Nodule Field (IONF). Since the 1970s, many processes for treating polymetallic nodules have been investigated. A recent comprehensive review of available processes can be found in an article by T. Abramovski et al., Journal of Chemical Technology and Metallurgy, 52, 2, 2017, 258-269. Kennecott and INCO attempted to develop industrial processes. Kennecott developed the Cuprion ammonia process, while several companies developed hydrometallurgical processes in sulfate, chloride, and nitrate media. INCO studied pyrometallurgical processes producing a matte. More recently, the production of an alloy has been proposed. None of these processes progressed beyond the pilot scale. The Cuprion process faces challenges with low Co recovery, slow nodule reduction by CO gas, and poor manganese residue quality. Sulfate processes derived from lateritic processes, which utilize autoclave leaching to reject Mn and Fe in the leach residue, encounter technological challenges in leaching, as well as poor Mn valorization. Other sulfate-based processes lead to high reagent consumption and / or the production of lethal ammonium sulfate. The ai / Lnn / zznz / e / Yi / u chloride and nitrate routes have high energy consumption for reagent regeneration via pyrohydrolysis and pyrolysis. Drying the nodules before pyrometallurgical processing also leads to high energy consumption. In this context, it is worth noting that US patent 3,906,075 discloses a single-stage leaching process using SO2 and sulfuric acid. Mn, Ni, Co, and Cu are leached simultaneously. This document also illustrates the crystallization of manganese as MnSO4, followed by its decomposition into oxide, thus generating SO2 for reuse in the leaching stage. The MnSO4 is added to the leaching stage because it is said to force the Fe to remain undissolved. The Cu is extracted from the single leachate stream. Liquid-liquid extraction is commonly used, although the cost and complexity of this process are considerable given the volumes to be treated. It has been recognized in the prior art that Fe in the leachate is undesirable, as a costly deferrization step would be required to clean the solution. Therefore, relatively mild leaching conditions are proposed, including the addition of high concentrations of MnSO4 to the leaching solution. It is assumed that the high SO4 concentrations may limit the solubility of Fe; however, then suboptimal recovery yields for Co and Ni are observed. This process, among others, is characterized by a very different approach to handling iron-related issues. There is absolutely no attempt to limit iron leaching during the mineral dissolution stage. On the contrary, the iron is dissolved and retained in solution until the MnSO4 crystallization stage. A mixed Mn-Fe residue is then obtained, which, after heat treatment, can yield an Mn-Fe oxide suitable for the steel or manganese industries. Excellent yields of copper, cobalt, and nickel are obtained, while the iron is leached and recovered along with the manganese. Figure 1 provides an overview of the flow diagram, including process stages and optional streams. The process stages are identified in Table 1 and the streams in Table 2. ai / Lnn / zznz / e / Yi / u Table 1: Identification of the process stages according to Figure 1 Process Stage ID Description P1 Dissolution of minerals P2 Cu recovery P3 Neutralization P4 Co and Ni Precipitation P5 Mn and Fe Crystallization Process Stage ID Description P6 Thermal Decomposition P7 Mn Precipitation (Purge) P8 Reverse Osmosis ai / Lnn / zznz / e / YiAi Table 2: Identification of product streams in Figure 1 Stream ID Type Description RO Feed Minerals R1 Residue First residue, mineral-insoluble compounds R2 Residue Second residue, when Cu is precipitated using H2S R3 Residue Third residue, when CaCO3 is used as a neutralizing agent R4 Residue Fourth residue, after Co and Ni are precipitated using H2S R5 Residue Fifth residue, after Mn and Fe are precipitated by crystallization R6 Residue Sixth residue, when Mn is precipitated from the purge stream R7 Residue Seventh residue, when the fifth residue is thermally decomposed Stream ID Type Description S1 Solution First solution, leaching solution containing Cu, Co, Ni, Fe, and Mn S2 Solution Second solution, containing Co, Ni, Fe, and Mn S3 Solution Third solution, neutralized, Co, Ni, Fe, and Mn S4 Solution Fourth solution, containing Mn and Fe S5 Solution Fifth solution,Mother liquors containing a small part of Mn and Fe S5a Solution First fraction of the fifth solution, recirculated to the dissolution stage S5b Solution Second fraction of the fifth solution, purge stream S6 Solution Sixth solution, depleted saline solution S7 Solution Seventh solution, essentially H2O S8 Solution Eighth solution, essentially a concentrated saline solution, The disclosed process suitable for the recovery of Cu, Co, Ni, Fe and Mn from oxide minerals comprises the stages of dissolving the minerals under acidic conditions, using H2SO4 and SO2, thus obtaining a first solution containing Cu, Co, Ni, Fe and Mn and a first residue, followed by S / L separation of the first solution and the first residue. A suitable extreme point pH for this stage would preferably be 2 or lower. Good leaching yields for the target metals, including Fe, are then observed. SO2 is injected directly into the leaching solution in an amount that is preferably stoichiometric with respect to the metals to be reduced. According to a first alternative, the Cu in solution can be recovered by precipitation as a sulfide by adding a sulfide-containing compound, or as a metal by adding a metal that oxidizes more easily than Cu, thus obtaining a second solution containing Co, Ni, Fe, and Mn and a second residue containing Cu and S / L separation of the second solution and the second residue. According to a second alternative, Cu can be recovered by extraction, using electrowinning or SX, thus obtaining a second acidic solution containing Co, Ni, Fe and Mn and a stream containing Cu. During this Cu recovery stage, the pH may decrease slightly due to the released protons, particularly when Cu is precipitated using H₂S or NaHS as the sulfide carrier. This decrease in pH has no detrimental effects other than requiring more acid-consuming compounds to act as neutralizing agents in the next stage of the process, which is the neutralization of the second solution to pH 2 to 5 by adding the first acid-consuming compounds, thus obtaining a third neutralized solution containing Co, Ni, Fe, and Mn. In a later stage, Co and Ni are precipitated by adding a sulfide-containing compound to the third solution, thus obtaining a fourth solution containing Fe and Mn, and a fourth residue containing Co and Ni, which are separated. During this Co and Ni recovery stage, the pH may decrease slightly due to the released protons. Additional neutralizing agents can be added to achieve a pH of 2 to 7. In fact, it is preferable to operate the next stage, which is the crystallization of Mn and Fe, using a neutralized solution to prevent equipment corrosion. ai / Lnn / zznz / e / YiAi In the neutralization stage, CaCO3 can be used as an acid-consuming compound. This produces gypsum, a solid that should preferably be separated in an additional solid-liquid separation stage. The production of solids requiring filtration can be avoided or minimized by using MnCO3 or Mn(OH)2 as a neutralizing agent. These two products can be advantageously generated in the treatment of a blowdown stream, as described below. The Mn and Fe are recovered together from the fourth solution by crystallization, thus obtaining a fifth solution (mother liquor) containing a smaller portion of the Mn, and a fifth residue containing most of the Mn and Fe. The crystals are then separated from the mother liquor. The crystallization of Mn and Fe can be carried out by evaporation. Alternatively, crystallization can be induced by heating, since the solubility limits of Mn and Fe decrease sharply with temperature. A temperature above 120 °C, or even above 170 °C, is therefore preferred. The mother liquors will still contain some residual dissolved Mn and Fe, as crystallization will not completely deplete these elements in the mother liquors. These metals can be recovered according to the following embodiment. In this document, the mother liquors are divided into a first and a second fraction, with the first fraction being recirculated to the dissolution stage. The Mn and Fe in the second fraction (purge stream) are precipitated as carbonates or hydroxides by the addition of acid-consuming compounds, such as NapCO3 or NaOH, thus obtaining a sixth solution depleted in Mn and Fe, and a sixth residue rich in Mn and Fe, which are separated. Referring to the above description, it is advantageous to recirculate these carbonates or hydroxides as acid-consuming compounds to the neutralization stage. The purge stream will also provide an outlet for minor elements such as Na and K, which could otherwise accumulate to undesirable levels when the process is run continuously. The secondary compounds that consume acid are advantageously Na- or K-based, since Ca-based compounds would lead to the dilution of Mn in the gypsum. Another embodiment relates to a process comprising the thermal decomposition of the fifth residue, thereby obtaining a seventh oxide residue ai / Lnn / zznz / e / Yi / u containing Mn and SO2, and the separation and recirculation of the SO2 to the dissolution stage. Thermal decomposition in this process is achieved by heating the product from 850 to 1000 °C. Another embodiment relates to a process comprising the reverse osmosis stages of the sixth solution, thereby obtaining essentially pure water and a concentrated saline solution. The water can be reused in an earlier stage, for example, to wash away waste, and is then recirculated to the mineral dissolution stage. The concentrated saline solution can be discharged. Another realization refers to any of the above processes, where the minerals are deep-water nodules. The following examples further illustrate the invention. Example 1: Neutralization using CaCO3 One kilogram (dry) of polymetallic nodules ground to a D50 of 100 pm is mixed with 3.1 L of water. The suspension is stirred continuously at 500 rpm and heated to 95 °C. Over 1.5 hours, a total of 510 g of SO2 gas is blown into the suspension. Subsequently, 280 g of H2SO4 is added slowly over 2 hours. During this addition, some SO2 is released from the solution, resulting in an effective consumption of 400 g. A pH of 1.6 is reached. The suspension is separated by filtration. The solution contains 9 g / L of H2SO4. The solids are washed. The copper in the solution is precipitated in a first precipitation of sulfide. The solution is then heated to 80°C and stirred continuously at 300 rpm. Argon is blown onto the surface of the liquid. For 2 hours, 6.2 g of H₂S (i.e., according to 100% stoichiometry) is bubbled through the solution. The suspension is filtered, and the solids are washed with water and dried in a vacuum oven at 40°C. This solution now contains 14 g / L of H₂SO₄. The solution must be neutralized to achieve successful precipitation of Ni and Co. To this end, the solution is heated to 75 °C, stirred at 300 rpm, and argon is blown onto the surface of the liquid. 51.2 g of CaCOa are suspended in 0.15 L of water. This suspension is slowly added to the solution. Gypsum forms and is separated. The pH of the solution then reaches the target value of 3. Ni and Co are recovered from the solution using NaHS. The solution is heated to 70 °C and stirred continuously at 300 rpm. Argon is blown onto the surface of the liquid. 264 ml of NaHS solution containing 38 g of ai / Lnn / zznz / e / Yi / u are added to the solution. S / L (i.e., according to a stoichiometry of 120%) at a rate of 3 ml / min. The suspension is filtered and the solids are washed with water and dried in a vacuum oven at 40 °C. The solution is loaded into an autoclave and heated to 176 °C. Under these conditions, the solubility of both MnSO4 and FeSCU decreases, resulting in their crystallization. The crystals are separated from the liquid phase by hot filtration to prevent crystal redissolution. The quantities and compositions of the different filtrates and residues are given in Table 3. The yields of the dissolution (P1) and precipitation (P2, P4, P5) stages are given in Table 4. ai / Lnn / zznz / e / YiAi Table 3: Quantities and compositions (solutions in 1 g / L, residues in g and % by weight) Stream ID Mass (g) Volume n(l) Mn Ni Co Cu Fe Si Al R0 1000, 0 - 29 1.3 0.2 5 1.2 6, 2 6, 3 2.7 S1 - 3.59 80 3.6 0.6 9 3.2 12 0. 0 2.2 R1 300.0 - 0.9 7 0.0 4 0.0 1 0.1 6 6, 4 21 6.4 S2 - 3.59 80 3.6 0.6 9 0.0 12 o P 2.2 R2 17.3 - 0.0 0.0 0.0 66 or or or or 0.0 S3 - 3.74 77 3.4 0.6 6 0.0 11 0, R5 900.4 5 - 28 0.0 0.0 0.0 4, 0 or P 0.7 Table 4: Metal yields (in %) by process stage Process Stage ID Mn Ni Co Cu Fe Si Al P1 99 99 99 96 69 0 29 P2 0 0 0 100 0 0 0 P4 0.1 100 100 100 1 0 14 P5 88 0 0 0 85 0 97 ai / Lnn / zznz / e / YiAi The metal yields per stage of the process are considered the most satisfactory. Example 2: Neutralization using MnCOs This example is analogous to example 1. However, the recirculated Mn and Fe carbonates are used as a neutralizing agent instead of CaCO3. Consequently, no gypsum is formed, and the corresponding filtration step is eliminated. After the precipitation of Cu, the solution needs to be neutralized. For this purpose, a fraction of the pumpable suspension, prepared as shown below, is slowly added to the solution as acid-consuming compounds. Upon adding an amount containing 58.8 g of a mixture of Mn and Fe carbonates, the pH of the solution reaches the target value of 3. Next, Mn and Fe are recovered by crystallization, according to example 1. The Mn and Fe still present in the mother liquors after the crystallization stage are precipitated as carbonates by the addition of 66.8 g of NazCOs. The suspension is filtered, and the residue is washed and dried. It contains 92.4 g of a mixture of Mn and Fe carbonates. This residue is then diluted with 0.28 L of water to create a pumpable suspension. Part of this suspension is used as acid-consuming compounds in the stage described above. It should be noted that in a continuous process, it would be advantageous to perform the precipitation stage on only a fraction of the mother liquor. This fraction is determined by the need for acid-consuming compounds in the neutralization stage. The remaining mother liquor can then be recirculated to the dissolution stage. The quantities and compositions of the different filtrates and residues are given in Table 5. The yields of the dissolution (P1) and precipitation (P2, P4, P5) stages are given in Table 6. Table 5: Quantities and compositions (solutions in 1 g / l, residues in g and % by weight) Stream ID Mass (g) Volume n(l) Mn Ni Co Cu Fe Si Al RO 1000, 0 - 29 1.3 0.2 5 1.2 6, 2 6, 3 2.7 S1 - 3.59 80 3.6 0.6 9 3.2 12 0. 0 2.2 R1 300.0 - 0.9 7 0.0 4 0.0 1 0.1 6 6, 4 21 6.4 S2 - 3.59 80 3.6 0.6 9 0.0 12 0, 0 2.2 R2 17.3 - 0.0 0.0 0.0 66 0, 0 0.0 0.0 S3 - 3.77 83 3.4 0.6 6 0.0 13 or or 2.1 S4 - 3.77 82 0.0 0.0 0.0 12 or P 1.8 R4 28.2 - 1.1 46 8.8 0.0 1, 7 0. 0 3.9 S5 - 3.67 10 0.0 0.0 0.0 1, 9 or, 0 0.0 6 R5 973.2 - 28 0.0 0.0 0.0 4, 1 0, 0 0.7 R6 58.8 - 40 0.0 0.0 0.0 7, 6 0, 0 0.0 ai / Lnn / zznz / e / YiAi Table 6: Metal yields (in %) by process stage Process Stage ID Mn Ni Co Cu Fe Si Al P1 99 99 99 96 69 0 29 P2 0 0 0 100 0 0 0 P4 0.1 100 100 100 1 0 14 P5 88 0 0 0 85 0 97 Although the yields per stage of the process are equally satisfactory 5 as in example 1, the overall yield of Mn will be higher when applying the neutralization method according to example 2. In fact, most of the Mn in the mother liquors after crystallization will be recovered in this case and extracted in the crystallization stage.

Claims

1. A process for recovering Cu, Co, Ni, Fe, and Mn from oxide minerals, comprising the steps of: - dissolving the minerals (P1) under acidic conditions using H2SO4 and SO2, thus obtaining a first solution (S1) containing Cu, Co, Ni, Fe, and Mn and a first residue (R1); - separating the S / L of the first solution and the first residue; - recovering Cu (P2) either by: - ​​precipitation as sulfide by adding a sulfide-containing compound, or as metal by adding a metal that oxidizes more easily than Cu, thus obtaining a second acidic solution (S2) containing Co, Ni, Fe, and Mn and a second residue (R2) containing Cu; and, - separating the S / L of the second solution and the second residue; or by: - ​​extraction by electrowinning or SX, thus obtaining a second acidic solution containing Co, Ni, Fe, and Mn and a stream containing Cu;- Neutralization (P3) to pH 2 to 5 of the second solution (S2) by adding the first acid-consuming compounds, thus obtaining a third neutralized solution (S3) containing Co, Ni, Fe, and Mn; - Precipitation of Co and Ni (P4) by adding a sulfide-containing compound to the third solution, thus obtaining a fourth solution (S4) containing Fe and Mn and a fourth residue (R4) containing Co and Ni; - Separation of the solids (S) from the fourth solution and the fourth residue; - Crystallization of Mn and Fe (P5) as sulfates from the fourth solution, thus obtaining a fifth solution containing a smaller portion of the Mn (S5), and a fifth residue containing most of the Mn and Fe (R5); and, - Separation of the solids (S) from the fifth solution and the fifth residue.

2. A process according to claim 1, wherein, in the neutralization step, the first acid-consuming compound contains calcium, in particular CaCO3, thereby obtaining a third residue (R3), and comprising the further step of: - S / L separation of the third solution and the third residue. ai / Lnn / zznz / e / Yi / u 3. A process according to claim 1 or 2, comprising the steps of: - splitting the fifth solution (S5) into a first (S5a) and a second fraction (S5b); - recirculating the first fraction of the fifth solution to the dissolution step (P1); - precipitating Mn and Fe (P7) as carbonates or hydroxides by adding second acid-consuming compounds to the second fraction of the fifth solution, thereby obtaining a sixth solution depleted in Mn and Fe (S6), and a sixth residue rich in Mn and Fe (R6); - separating the S / L of the sixth solution and the sixth residue; and - recirculating the sixth residue to the neutralization step (P3), as at least some of the first acid-consuming compounds.

4. Process according to any one of claims 1 or 3, comprising the steps of: - thermal decomposition (P6) of the fifth residue, thereby obtaining a seventh oxide residue (R7) containing Mn and SO2; - separation of the SO2; and; - recirculation of the SO2 to the mineral dissolution stage (P1).

5. Process according to any one of claims 1 or 4, comprising the steps of: - reverse osmosis (P8) of the sixth solution, thereby obtaining water (S7) and concentrated saline solution (S8); and, - recirculation of the water to the mineral dissolution stage (P1).

6. Process according to any one of claims 1 to 5, wherein the minerals are deep-water nodules.